In recent years, demand for a plated steel sheet having improved corrosion resistance or the like, improved appearance, and specially used as a steel sheet for electronic products and vehicles, has increased. For example, an alloy-plated steel sheet has excellent spot weldability, corrosion resistance after coating, and coating adhesion. Thus, demand for such a steel sheet for use in building materials, home appliances, and vehicles has recently increased.
FIG. 1 is a schematic view illustrating a general plating line for a steel sheet, and FIG. 2 is a plan view illustrating a cooling fluid being sprayed onto a plated steel sheet by a plated steel sheet cooling apparatus according to the related art.
With reference to FIG. 1, after a steel sheet 1 (a cold-rolled steel sheet) unwound from a pay-off-reel passes through a welder and a looper and heat-treated molten metal, for example, molten zinc 3, is attached to a surface of the steel sheet 1 while the steel sheet passes through a snout, below a sink roll 4 and through stabilizing rolls 5 of a plating bath 2. In addition, a high pressure gas (inert gas or air) is sprayed from a gas wiping device 6 (commonly referred to as an ‘air knife’) above a plating bath to control a plating thickness of the steel sheet 1.
In addition, the plated steel sheet 1 is plated while passing through a vibration damping facility 7, a cooling facility 8, and transferring rolls 9. The vibration damping facility suppresses vibrations of the steel sheet 1 passing through a gas wiping region to uniformly control a plating thickness.
Here, the cooling facility 8 is provided on both sides of the steel sheet 1 being vertically transferred according to the related art, and thus, the cooling facility may be referred to as a cooling tower.
Such a cooling facility 8 of the plated steel sheet is an important facility in solidifying a zinc-plated layer in a liquid phase attached to a surface of a high-temperature plated steel sheet being vertically transferred, and quickly cooling a temperature of the steel sheet 1 to be 300° C. or less immediately before the transferring roll 9 to smoothly perform transferring or a post process of the steel sheet 1 thereafter.
In this case, as illustrated in FIG. 2, a cooling facility according to the related art may include spraying nozzles 13 provided in a predetermined pattern in nozzle chambers 12 opposing each other on both sides of a steel sheet 1.
However, an arrangement width of the spraying nozzles 13 is fixed to be relatively greater than a maximum width L1 of the steel sheet 1 to be plated and produced. Thus, in a case in which the width L1 of the steel sheet 1 to be plated is narrower than a width L2 of a region in which cooling fluids are sprayed through the spraying nozzles, in regions ‘A’ in which the steel sheet 1 is not present, the cooling fluids sprayed at a high pressure collide with each other, thereby amplifying a vortex.
Such vortex amplification allows vibrations of an edge portion to be amplified in both edges of the steel sheet 1 while being vertically transferred.
Such an increase in the vibrations of the steel sheet 1 may cause various problems in a plating line. As tension applied to the stabilizing rolls 5 or the transferring rolls 9 for a reduction in the vibration of the steel sheet is increased, abrasion of the rolls may be increased and a cooling performance may also be reduced. In addition, as it may be difficult to increase a plating rate of the steel sheet 1 due to the vibrations of the steel sheet, productivity may be reduced.
In addition, as illustrated in FIG. 2, in a case in which a narrow plated steel sheet is produced, an excessive amount of cooling fluids is sprayed even to areas in which the steel sheet 1 is not present in a width direction. Thus, an air blower may be overloaded and a cooling efficiency thereof may be reduced, which may be various causes of a reduction in productivity.